WHALES, GIANTS OF THE SEA
La Plata Dolphin
(Stenodelphis blainvillii)
Among the lesser-known kinds of dolphins
that are found solely in the Southern Hemi
sphere, the La Plata Dolphin is recognized as
being the most specialized, not only in its
skeletal construction but in its outward form
(Plate XV). It seems to prefer the estuaries
of fresh-water rivers, but appears occasionally
in coastal waters on the Atlantic side of South
America.
The record length and weight for a female
are respectively 68 inches and 88 pounds; full
grown males are at least 6 inches shorter and
weigh approximately 70 pounds. Their dull
coloration, small size, and unobtrusive habits
tend to render them quite inconspicuous and
protect them from the attacks of some of their
more cannibalistic relatives. They travel, feed,
and breed in small schools. The newborn
young are surprisingly small, measuring about
18 inches in length and weighing 15 pounds.
La Plata Dolphins delight in coming along
side fishing boats and thus are readily captured
by fishermen. They rarely are seen in the
Plata estuary during the winter. Perhaps at
this season most of the schools migrate north
ward along the Brazilian coast or frequent the
high seas in approximately the same latitude.
Their teeth, quite long, slender as toothpicks,
and sharply pointed, are marvelously adapted
for catching and holding soft-bodied prey.
The food of this dolphin consists chiefly of the
silvery mullet which swim in shoals and cer
tain croakerlike fish which are noted for their
ability to make a drumming noise.
Amazon River Dolphin, or Bouto
(Inia geoffrensis)
Geological ages ago, as shown by fossils, the
family Iniidae, to which this river-dwelling
dolphin belongs, was widely distributed in the
waters of the world, but today there are only
two survivors, the White Flag Dolphin in Tung
Ting Lake, China (Plate XXIII), and the
Bouto in South America (Plate XV).
All reports indicate that these dolphins are
numerous in the Amazon River, from the long
reach where the Tocantins empties into it,
to and including most of its principal tribu
taries. The Boutos travel upstream at least
to Nauta. Peru, on the Marafi6n,
and follow
some of the latter's smaller tributaries to lakes
at the foot of the Cordilleras.
In Bolivia thev inhabit the rivers that drain
the immense Plains of Mojos and empty into
the Guapore and Mamore Rivers, several hun
dred miles upstream from the falls on the
Madeira.
They ascend the Purus at least
as far as Hyutanahan, penetrate far up
stream in the Negro and the Branco, and
enter some of the smaller tributaries of these
rivers.
They have been seen in the Tacutu River,
which forms part of the boundary between
British Guiana and Brazil. On the Venezuela
border, the Casiquiare River connects the
Negro with the Orinoco, and through this chan
nel the Bouto makes its way from the Amazon
to the Orinoco.
The Boutos in the large rivers generally have
pale-bluish, bluish-gray, or even flesh-colored
upper parts, but those that wander into the
larger lakes during the season of heavy rains
are often blackish. The underparts are paler,
usually whitish but sometimes pinkish.
Full-grown males attain a length in excess of
nine feet. The slender and almost cylindrical
beak is curved slightly downward. The Bouto
comes to the surface to breathe more fre
quently than the oceanic dolphins. It feeds on
fresh-water fish, including those that are habitu
ally found on river bottoms.
White-beaked Dolphin
(Lagenorhynchus albirostris)
One of the most abundant of all the North
Atlantic toothed whales is the White-beaked
Dolphin, which seems to prefer the colder
northern waters from southern Greenland as far
north as Sukkertoppen, on Davis Strait, and
the Tromso coast of Norway (Plate XVI).
Schools are present in the North Sea through
out the year. On the American side of the
Atlantic they are rarely seen south of Labrador.
The White-beaked Dolphin may be recog
nized at once by its white beak, about two
inches long, separated from the sloping fore
head by the usual cross groove. The dark
color of the upper parts usually extends down
ward to the base of the blackish upper surface
of the rather broad flippers. Old adults rarely
exceed 10 feet in length.
This dolphin is protected from the cold of
the northern waters by a thick coating of
blubber. Vast schools of as many as 1,500 or
more are often seen. Stomachs of these ani
mals have been found packed with the undi
gested bones of whiting, claws of hermit crabs,
and horny parts of the common whelk, a mol
lusk used in dyeing purple. They also feed
on capelin, cod, squids, and crustaceans.
White-sided Dolphin
(Lagenorhynchus acutus)
Both summer and winter, schools of White
sided Dolphins roam about in the North At
lantic Ocean. from southern Greenland and
the North Sea as far north as the Arctic
Circle on the coast of Norway, and south
to the British Isles, the Netherlands, and Cape
Cod, Massachusetts (Plate XVI).
This dolphin is readily recognized by the
lighter area on each side of the body below the
dorsal fin, and by the conspicuous elongated
yellowish-brown and grayish lateral streaks
above the white underparts. Its beak is about